Several isozymes of mammalian type 2, Mg(2+)-independent phosphatidic acid phosphatase (PAP-2) have recently been cloned, and they are predicted to have their catalytic sites exposed at the cell surface membranes. We investigated the mode of utilization of extracellular lipid substrates by the human PAP-2b expressed in HEK293 cells as a green fluorescent fusion protein. We first confirmed the plasma membrane localization of the expressed PAP-2b. PAP-2b actively hydrolyzed exogenously added lysophosphatidic acid and short-chain phosphatidic acid. In the case of dephosphorylation of lysophosphatidic acid, the reaction products, including inorganic phosphate and monoacylglycerol, were recovered exclusively in the extracellular medium. Interestingly, PAP-2b exhibited negligible activities toward long-chain phosphatidic acid either exogenously when added or generated within the membranes by treating the cells with bacterial phospholipase D. These findings indicate that PAP-2b acts at the outer leaflet of cell surface bilayers and can account for the ecto-PAP activities previously described for various types of cells.

Dasatinib treatment markedly increases the number of large granular lymphocytes (LGLs) in a proportion of Ph leukemia patients, which associates with a better prognosis. The lymphocytosis is predominantly observed in cytomegalovirus (CMV)-seropositive patients, yet detectable CMV reactivation exists only in a small fraction of patients. Thus, etiology of the lymphocytosis still remains unclear. Here, we identified NK cells as the dominant LGLs expanding in dasatinib-treated patients, and applied principal component analysis (PCA) to an extensive panel of NK cell markers to explore underlying factors in NK cell activation. PCA displayed phenotypic divergence of NK cells that reflects CMV-associated differentiation and genetic differences, and the divergence was markedly augmented in CMV-seropositive dasatinib-treated patients. Notably, the CMV-associated highly differentiated status of NK cells was already observed at leukemia diagnosis, and was further enhanced after starting dasatinib in virtually all CMV-seropositive patients. Thus, the extensive characterization of NK cells by PCA strongly suggests that CMV is an essential factor in the NK cell activation, which progresses stepwise during leukemia and subsequent dasatinib treatment most likely by subclinical CMV reactivation. This study provides a rationale for the exploitation of CMV-associated NK cell activation for treatment of leukemias.

No abstract

This is the first report evaluating rTM administration for TA-TMA compared with previous treatments. Our data suggests that rTM might offer a better clinical outcome in patients with TA-TMA.

No abstract